The present invention relates to a light emitting diode and the method for making the same, especially to a light emitting diode with inorganic phosphor having modified surface property to enhance yield.
The white light LED developed by Nichia company is composed of a blue LED generally made of InGaN and a yellow inorganic phosphor made of YAG (yttrium aluminum garnet). The yellow inorganic phosphor is excited by blue light from the blue LED and emits yellow light, which is mixed with the blue light to generate white light. The white light LED typically shows a color temperature of 8000 K at a forward current of 20 mA. The color rendering index (CRI) of the white light LED is comparable with the fluorescent lamp and the efficiency of the white light LED is comparable with light bulb (5-10 lm/W) and fluorescent lamp (10-30 lm/W).
In comparison with the LED set composed of three primitive colors (red, green and blue), the white light LED using yellow phosphor has advantages of simple structure and low cost. The color degradation probability due to failure of LED of respective color can be reduced. The white light LED is a light source with high directiveness and can be used for vehicle panel lighting, backlight of LCD, room lightening, notebook computer display, scanner, FAX, projector and cellulous phone.
The white light LED also has the advantages of compactness, long life, low current/voltage, no thermal radiation, and power saving and is expected as light source replacement for conventional light bulb.
The yellow YAG phosphor in the white light LED of Nichia company is firstly mixed with resin with suitable ratio and is then packaged with a blue LED. The yellow YAG phosphor is an inorganic compound, which is hard to mix with the organic resin. Moreover, the weight ratio of the yellow YAG phosphor and the organic resin is also large such that it is hard for the yellow YAG phosphor powder to suspend in the organic resin.
To overcome above problem, resin of high viscosity or other type of glue are used to mix with the YAG phosphor. The glue can be classified into two types, inorganic and organic. For example silicone is an inorganic glue with high viscosity. However, the transparency is only 80% and the applicability thereof is limited. For organic glue such as epoxy resin, the epoxy resin with high viscosity is commercially available with lower price. However, the allowable processing time is short.
The above-mentioned glues with high viscosity can prevent the phosphor powder from deposition. However, the above-mentioned glues have following drawbacks:
(1) The glues with high viscosity cannot be mixed uniformly with the phosphor powder.
(2) For the glues with high viscosity, the amount thereof is hard to control and the yield is influenced.
It is the object of the present invention to provide an LED to overcome above problems and having enhanced yield and brightness.
To achieve above object, the present invention provides an LED comprising an inorganic phosphor, a silicon compound and an organic glue. The silicon compound has one side being completely or partially C1-C6 alkyl oxide reacted with the inorganic phosphor to modify the surface property of the inorganic phosphor and another side being a functional group selected from a group consisting of epoxy, C1-C6 alkyl, phenyl, amino. The inorganic phosphor with modified surface property can be uniformly mixed in the glue and less deposition is produced.